If youre using lots of different kinds of pockets and having trouble with all of them then it probably is the inserts you should be looking at. Perhaps start with some easy peasy hemp boosters to use underneath the microfiber inserts - these are slimmer than bamboo and might help with the gaping. You can get them quite cheaply on eBay. I'm thinking change as little as possible to start with rather than going out and buying a whole heap of new nappies and inserts (though if you fancy shopping...)
I have the petit dissou bamboo inserts that lots of people here have and find these work well with all my pockets. They will go about 2 hours on their own and if I add an EP hemp booster then I can get 3hrs plus.
How often are you changing? Perhaps just changing more often would allow you to use less bulk and get a better fit?
I also have some hemp inserts (I have happy heiny stuffins) and use the BG microfiber inserts on top of those sometimes too. You can't really use hemp on its own as it is quite slow to absorb and the wee can just run off it.
I've just been looking for inserts for you and come accross www.funkymonkeypants.com
(warning very dangerous site
) and they have a very good collection of inserts and boosters. Baby kind also has quite a few. Or just keep an eye on classifieds.